I don't think there's an official form for when someone turns in an expense with no receipt, though some wards might have a form they created to use. Basically you just need a paper that says the amount spent, when and where, why you didn't get a receipt, and a signature...

If the original receipt or invoice is lost, the substitute documentation should include a written explanation with the payment purpose, a description of what was bought or paid for, the date the payment was made, the name of the person assisted (for payments from fast offerings), and proper approval.

Any prepared form should have provisions for those five (six for fast offering payments) required items at a minimum. Essentially the substitute documentation would have the same things a receipt would have with the addition of an explanation and proper approval.